In Slicedlime's dump of the vanilla features, the fancy_oak.json claims that it is using blob_foliage_placer as foliage_placer but it is actually using large_oak_foliage_placer.

This error comes from the fact that the LargeOakFoliagePlacer is extending BlobFoliagePlacer (unclear as to why this is the case), while not overriding the getType (yarn mapping) method.